Method for frequency compensating a magnetron anode for temperature change



Oct. 15, 1957 P. P. DERBY ETAL 2,810,094

METHOD FOR FREQUENCY. COMPENSATING A NETRON ANODE FOR TEMPERATURE CHANG Filed Oct. 11. 1955 MAGNETRON ANODE RESONATOR INVENTORS,

PALMER F. DERBY LEONARD W. GEIER United States Patent M METHOD FOR; FREQUENCY COMPENSATING A ggggggxol ANODE FOR TEMPERATURE Palmer P. Derby, Weston, and Leonard W. Geier, Natick.

Mass., asslgnors to the United States of America as repted by t e Sec e a y of e rmy pp ion Oct be .11, 1955, Serial No. 539,

8 Claims. (Cl. 315-e 3951) This invention relates to electron discharge devices for use at ultra high frequencies, and more particularly to magnetrons having vane-type resonator structures.

The resonant determining structure of conventional vane-type magnetrons comprises a cylindrical anode block wherein the vanes and anode cylinder are made of the same metallic material, usually copper, or some copper alloy such as 20% or 30% cupro-nickel. In such devices it is well known that due to the thermal expansion characteristics of the anode block, temperature variations will produce undesired variations in the output frequency. As the temperature of the entire structure rises the an ode cylinder will expand outwardly from the center thereby causing the inductance of the cavity to increase and thus produce a decrease in the resonant frequency. Heretofore, such variations in frequency were compensated for by utilizing temperature compensating devices which include an axially disposed movable disc spaced from one end of the anode block. The addition of this type of tuning element necessarily complicates the fabrication of such magnetrons inasmuch as the initial spacing between the temperature compensated tuning element and the anode block must be carefully adjusted to provide the correct resonant frequency.

It is an object of the present invention to provide a novel temperature responsive frequency compensating means which is an integral part of the magnetron anode resonator.

It is another object of the invention to provide a magnetron resonant anode structure wherein the temperature responsive frequency tuning element is completely eliminated.

In accordance with the present invention there is provided a magnetron anode resonator comprising a cylindrical body and a plurality of inwardly extending radial vanes. The cylindrical body and the vanes are made of metals having discrete linear thermal coefiicients of expansion. The thermal coefficient of expansion of the metal constituting the cylindrical body is greater than that of the metal constituting the vanes. Due to the unequal thermal expansion of the cylindrical body and the vanes, the increased inductance due to the expansion of the anode cylinder caused by rising temperatures is compensated for by a decrease in capacitance caused by the vane tips being spread further apart.

For a better understanding of the present invention together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing which shows, in cross section, the magnetron anode resonator structure embodying my invention.

Referring now to the drawing, at 10 there is shown an anode resonator structure for a magnetron comprising the anode cylinder 12 and a plurality of inwardly extending radial vanes 14. Anode cylinder 12 is fabricated from one type of conductive material, and the vanes 14 are made of a different type of conductive material and brazed in the usual manner to the inner surface of cylin- 2,810,094 Patented Oct. 15, 1957 der 12 The conductive materials are chosen such that the linear coefficient of thermal expansion of anode cylinder 12 is substantially greater than the linear coeflicient of thermal expansion of vanes 14. For example, anode cylinder 12 may he made of 20% or 30% cupro-nickel both of which have a coefficient of thermal expansion of approximately 16 10= -/"C. and the vanes may be made of molybdenum which has a coefficient of thermal expansion of approximately 5 10-6/ C. Another suitable conductive material for the anode cylinder is Telnic Bronze, a copper alloy consisting of 98.3% copper, 1% nickel, 0.2% phosphorous, and 0.5% tellurium, and having a coefficient of thermal expansion slightly higher than either of the cupro-nickel alloys.

If LT1 and GT1 are the respective inductance and capacitance of the anode resonator 10 at temperature T1, and Lu and GT2 are the respective inductance and capacitance of anode resonator 10 at a higher temperature T2 then, for the frequency at T1 to equal the frequency at T2, LT1CT1=LT2CT2. It follows from this equation that to maintain a stabilized frequency, it becomes necessary for 0:2 to decrease, inasmuch as Lrz has increased. Due to the unequal thermal expansion of the anode cylinder 12 and the vanes 14, the outward expansion of the anode cylinder from the center due to increased temperature will be greater than the linear expansion of the vanes. By this arrangement, the vane tips are moved further apart as the temperature of the resonator rises. Thus, the increase of inductance due to the expansion of the anode cylinder at the higher temperature T2 is compensated for by the decrease in capacitance at temperature T2 due to the vane tips being spread further apart. When the anode resonator having an anode cylinder of cupro-nickel and vanes of molybdenum was incorporated in a conventional magnetron, the thermal coefiicient of the tube was found to be 0.179 mc./ C. For the anode cylinder made of Telnic Bronze, the thermal coefficient of the tube was found to be O.l2 mc./ C. In the latter case, greater frequency stability was achieved because the anode cylinder was made of a material having a higher coeflicient of expansion.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A magnetron anode resonator structure comprising a cylindrical body and a plurality of inwardly extending radial vanes respectively made of metals having discrete thermal coefficients of expansion, the thermal coefficient of expansion of the metal constituting the cylindrical body being greater than that of the metal constituting the vanes.

2. The device in accordance with claim 1 wherein said vanes are made of molybdenum.

3. In a magnetron, an anode resonator comprising a cylindrical body and a plurality of inwardly extending radial vanes and adapted to resonate at a prescribed frequency at a given temperature, the tips of said vanes having a prescribed uniform circumferential spacing at said temperature, said cylindrical body and said vanes being respectively made of metals having different thermal coefiicients of expansion such that the circumferential spacing of said vane tips is varied with changes in temperature.

4. In a magnetron, an anode resonator comprising a cylindrical body and a plurality of inwardly extending radial vanes and adapted to resonate at a prescribed frequency at a given temperature, the tips of said vanes having a prescribed uniform circumferential spacing at said temperature, said cylindrical body and said vanes being made of dissimilar metals, the thermal coefficient of cxpansion of the metal constituting said cylindrical body being of a greater value than the thermal coefiicient of expansion constituting said vanes such that the uniform circumferential spacing of said vane tips is increased with a rise in temperature whereby said frequency is main tained substantially constant for the variation in temperature.

5. The device in accordance with claim 1 wherein said cylindrical body is made of a copper alloy consisting of 98.3% copper, 1% nickel, 0.2% phosphorous and 0.5% tellurium.

til.

6. The device in accordance with claim 1 wherein said cylindrical body is made of a copper alloy consisting of 80% copper and 20% nickel.

7. The device in accordance with claim 1 wherein said cylindrical body is made of a copper alloy consisting of 80% copper and 20% nickel and said vanes are made of molybdenum.

8. The device in accordance with claim 1 wherein said cylindrical body is made of copper alloy consisting of 98.3% copper, 1% nickel, 0.2% phosphorous and 0.5% tellurium and said vanes are made of molybdenum.

References Cited in the tile of this patent UNITED STATES PATENTS 2,753,486 Phillips July 3, 1956 

